This invention relates to an apparatus and method for an active vibration control device and, more particularly, to such an apparatus and method adapted to reduce vibration in a machine tool member.
Excessive vibrations frequently called "chatter" between the cutting element of a machine tool and the surface of the workpiece cause poor surface finish, tool breakage and other undesired effects that have long plagued machining operations. Such vibrations arise especially when the tool includes a long unsupported length that will permit deflection of the tool. When chatter does occur the machining parameters must be changed and as a result productivity may be adversely affected.
When using the stiffest and most advanced machine tool design, there still remains vibration in the machine tool. For example, a long cantilevered boring bar with a single cutting element at its free end will, by its interaction with the workpiece, tend to vibrate.
This vibration may be considered to be self-excited because it is generated by the interaction of the cutting element and the workpiece. Such self-excited vibration occurs at frequencies near the natural frequency of the cantilevered tool and, therefore, tends to increase in amplitude under small disturbing forces.
While the amplitude will generally be greatest at the free end of the tool, the pattern of vibration, such as the spacing of the nodes and the kind of harmonics generated, may vary widely under different conditions and from one point along a workpiece to another. It will be understood the "vibration" as employed herein does not refer to simple deflection or yielding of the tool which may be brought about simply by large static forces developed thereon, but refers to vibrations or oscillations which tend to be maintained or increased when energized by a selectively small oscillation in the disturbing force. Such a disturbing force usually corresponds to a resonant condition.
It is among the general objects of this invention to provide an active vibration control device that will substantially reduce or eliminate chatter and vibration, especially of the self-excited type, in machine tool members.
Another object is to provide an improved active vibration control device that will be effective over a wide range of frequencies.
Another object is to provide an improved active vibration control device that will oppose motion in a vibrating member by inertial changes of an inertial element.
Another object is to provide an improved active vibration control device in the form of a convenient package that will be effective in a wide variety of applications and have advantages not found in existing devices.
Still another object is to provide a method of actively controlling vibration which is more effective than previously known methods.